Friction material

ABSTRACT

1. A COMPACTED FRICTION MATERIAL COMPRISING NICKEL SULPHIDE FORMED IN SITU FROM 15% TO 85% BY WEIGHT OF FINELY DIVIDED NICKEL AND 5% TO 65% BY WEIGHT OF ANTIMONY SULPHIDE, AND 5% TO 45% BY WEIGHT OF AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF FILLERS AND FRICTION MODIFIERS.

3,842,031 FRICTION MATERIAL John B. Lumb, Bradford, and Michael Edwards,Leeds,

England, assignors to BBA Group Limited, Cleckheaton, Yorkshire, EnglandNo Drawing. Continuation-impart of application Ser. No. 133,765, Apr.13, 1971, now Patent No. 3,723,382. This application Nov. 28, 1972, Ser.No. 310,001 Claims priority, application Great Britain, Nov. 29, 1971,55,315/ 71 The portion of the term of the patent subsequent to Mar. 27,1990, has been disclaimed Int. Cl. C08g 51/04 US. Cl. 260-38 15 ClaimsABSTRACT OF THE DISCLOSURE A friction material for friction braking ortransmission systems including in its finished state a two-part bindersystem, one part being constituted by a thermosetting resin and theother part being constituted by two materials which react together underthe action of heat generated during application of the system to form acompound which provides additional binding for the material andcompensates for thermal decomposition of the resin. In one embodimentthe two materials are nickel and sulphur, and in another embodiment thetwo materials are nickel and antimony sulphide. In both embodiments thetwo materials react to form nickel sulphide in situ. Friction modifiers,fillers and reinforcing materials such as asbestos can be included inthe friction material of each embodiment. In a third embodiment, nothermosetting resin is used, the friction material being constituted bynickel sulfide formed in situ from nickel and antimony sulfide, togetherwith a filler and/or a friction modifier. A reinforcing material such asasbestos can be included if desired.

CROSS-REFERENCE This Patent Application is a Continuation-in-part of ourearlier Patent Application Ser. No. 133,765, now US. Patent 3,723,382.

This invention relates to friction materials which are particularlyintended for use in providing contact surfaces in friction braking ortransmission systems such for example as used in disc brakes, internalshoe drum brakes, clutch facings, and railway brake blocks.

Hitherto, such friction materials have usually consisted of mixtures offibrous material, generally fibrous inorganic material, such as asbestosfibre, metallic and non-metallic fillers, binders, and frictionmodifiers, the mixture being moulded into a dense state by theapplication of heat and pressure.

Friction materials which are to be used in disc brakes are subjected toconsiderably higher temperatures and pressures than the material whichis intended for use in drum brake installations, and consequently havehigher rates of wear. Moreover, the highest temperatures can also leadto a thermal breakdown of the binder material, which causes thecoefiicient of friction of the material to decrease. The reduction inthe coeflicient of friction of the material, which sometimes occursduring heavy and continuous braking, is referred to as fade.

It is a main object of the present invention to provide an improvedfriction material which is less susceptible to United States Patent fadethan previous friction materials which include thermosetting resins.

A further object of this invention which is fulfilled by one of theembodiments thereof is to provide a friction material in which the useof a thermosetting resin as binder is eliminated.

A still further object of the invention, which is fulfilled by otherembodiments, is to provide a friction material in which deterioration ofthermosetting resin binder in the friction material is compensated forby the formation of an additional binder, this binder being formed insitu during use of the friction material.

Our investigations have suggested that, in friction materials whichincorporate only conventional thermosetting resin binders, the heatgenerated under heavy and prolonged braking is often sufficient todecompose the thermosetting resin on the contacting surfaces of thefriction material, and this results in fade and high rates of wear.According to one aspect of our invention, we provide a friction materialfor use in friction braking or transmission systems which frictionmaterial contains a two-partbinder system, one part comprising athermosetting resin, and the other part comprising a mixture of at leasttwo materials which combine progressively by reacting with each otherunder the action of heat developed as a result of the frictionalengagement of the friction material within the system, to provideadditional binding for the friction material and thereby to compensatefor any deterioration in friction or wear characteristics of thefriction material as a result of thermal decomposition of thethermosetting resin.

We have found that finely-divided nickel and sulphur are particularlysuitable materials for incorporation in the friction materials.Alternatively, nickel and antimony sulphide can be incorporated in thefriction material. Both these pairs of substances react together to formnickel suphide when heated to a temperature such as is developed infriction braking or transmission systems as a result of prolongedapplication of the system. When the two materials are incorporated in afriction material, the nickel sulphide generated by reaction of thenickel and sulphur or nickel and antimony sulphide forms a matrix whichbinds together the friction material and thereby prevents furtherdeterioration of the friction material.

Depending on the method by which the friction material is manufactured,the nickel and sulphur or nickel and antimony sulphide may be wholly orsubstantially wholly uncombined in the finished friction material, orthey may have partially reacted with each other to form nickel sulphidein situ, any uncombined nickel and sulphur or antimony sulphide in eachcase being capable of reaction to form a nickel sulphide binder underthe action of heat developed as a result of frictional engagement.

The aforementioned friction materials of the present invention mayfurther include, if desired, a fibrous reinforcing material such asasbestos, one or more fillers and/or one or more friction modifiers. Thefiller may be a metal, such as brass powder or a non-metallic materialsuch as calcium carbonate powder, rottenstone or any other well-knownfiller. A friction modifier may be incorporated into the material inorder to help to maintain the coeificient of friction of the material ata desired level over a range of temperatures. Thus, an abrasive frictionmodifier such as alumina, and/ or Carborundum powder, can beincorporated in the mixture to increase the coefiicient of friction ofthe final material, or

a lubricative friction modifier, such as graphite or barytes, may beincorporated to reduce the coefficient of frictlon of the finalmaterial.

The thermosetting resins which may be incorporated in a frictionmaterial according to the invention are preferably phenolicthermosetting resins and include organic resins such as phenolformaldehyde and organic reslns which have been modified by thesubstitution of inorganic groups on to the organic molecule e.g. boratedphenolic resins. Mixtures of different thermosetting resins of eithertype may also be used in a friction material according to the presentinvention.

Friction materials incorporating nickel and sulphur may be manufacturedin accordance with this invention by mixing finely divided nickel andsulphur, asbestos, or other inorganic fibrous material with athermosetting resin, compressing the mixture, and heating the compressedmixture to a temperature sufficiently high to cure the resin e.g.between 120 C. and 180 C. Preferably, the heating is carried out in twostages, first by applying sufficient heat partly to cure thethermosetting resin whilst compressing the mixture, and subsequentlyheating the mixture after compression in order to complete the curing ofthe resin. After curing at these temperatures, the finished frictionmaterial will contain little or no nickel sulphide. However, nickelsulphide will be formed from the nickel and the sulphur under the actionof heat developed as a result of the frictional engagement of thefriction material within the friction braking or transmission system.

An alternative manufacturing process, however is to cure the compressedmixture at sufliciently high temperatures to cause at least some of thenickel to react with at least some of the sulphur to form nickelsulphide. At manufacturing temperatures in excess of 250 C., and inparticular in the region of 300 C., the nickel and sulphur in thefinished friction material will be wholly or substantially whollypresent as nickel sulphide, and no further reaction will take place inthe friction material when it is used.

In a preferred method of forming friction material according to thepresent invention inorganic fibrous material, fillers, thermosettingresin, finely divided nickel, sulphur and any desired friction modifiersare all intimately mixed together in a mixer or blending machine. Amoulding operation is then carried out in which a mould, for example, adisc pad mould, is charged with the mixture. The mixture is then curedby the application of heat and pressure. Generally the curing time is inthe order of five to ten minutes and the pressures which are applied tothe mould are from /2 to ten tons per square inch. It will beappreciated that the precise temperatures and pressures used in themoulding operation depend upon the relative quantities of theconstituents of the friction material.

The initial application of heat and pressure causes the mixture partlyto cure. The composition of the partly cured mixture depends upon thetemperature and the length of time for which the mixture was cured.Thus, the temperature and curing period in the moulding operation mayonly be sufliciently high to initiate curing of the thermosetting resin.For example, the temperature on the face of the mould may be between 120and 180 C. Alternatively, if higher temperatures are used, for examplein excess of 250 C., combination of the finely divided nickel with thesulphur to form nickel sulphide may be initiated. The partly-curedmixture is then removed from the mould and heated in an ovensufficiently to complete the curing process. For example, thepartlycured mixture may be heated for two to twenty-four hours at atemperature of from 90 to 300 C. Depending on the temperature selected,the finished product will contain completely cured thermosetting resin,the nickel and sulphur being either uncombined or partly or completelycombined as nickel sulphide.

An example of the ingredients (in parts by weight) from which frictionmaterial according to the present 1nvention may be made is shown:

An example of friction material made according to the present inventionis shown below:

Ingredient Parts by weight Asbestos fibre 25 Phenolic resin 8 Nickel l5Sulphur 6 Brass powder 10 Graphite 6 Barytes 24 The ingredients wereweighed out and mixed together in a blending machine for thirty minutes.The materials were then charged into a disc brake pad mould, and mouldedin a press at a temperature of 155 C. and at a pressure of one ton persquare inch for ten minutes. The material was then removed from themould, placed in an oven and heated at a temperature of 180 C. for tenhours.

The nickel and sulphur contained in the finished material were mainlypresent as the uncombined elements.

The materials were tested on an inertia dynamometer in order toinvestigate their wear characteristics as folows:

Two pads of the friction material each having an area of five squareinches were used as brake pads in an automobile disc brake caliper, eachpad being located on a respective side of a 10 inch diameter brakingdisc.

The material was subjected to a test schedule of 150 applications inwhich the rate of rotation of the disc was equivalent to road speeds ofup to m.p.h. Under these condltions kinetic energy of up to 40X 10 ft.lb. f. was dissipated. During part of the test, torque was maintained at400 lb. f. ft. and during the remainder it varied between and 600 lb. f.ft. The temperature measured on the face of the braking disc during thetest schedule varied from ambient to 400 C. The average wear on each ofthe disc pads after the test schedule was 0.005 inches.

A conventional friction material based on asbestos and a thermosettingresin was subjected to an identical test schedule and the average wearon each of these disc pads was 0.030 inches.

In order to manufacture a friction material in accordance with thisinvention which is based upon nickel, antimony sulphide and athermosetting resin, finely divided nickel, curable thermosetting resin,and antimony sulphide are mixed together. The mixture is then compressedand heated to a temperature sufficiently high to cure the thermosettingresin. Although the manufacturing conditions in this method need not besufiiciently extreme to cause the nickel and the antimony sulphide toreact to form nickel sulphide, under operating conditions, the surfacetemperatures, generated in the friction materials would be sufficientlyhigh to effect this reaction between the nickel and the antimonysulphide. Since conventional thermosetting resins usually begin todecompose at temperatures greater than 300 C., it will be appreciatedthat the formation of the nickel sulphide when the pad is in use shouldbegin at approximately the same temperature as that at which thethermosetting resin binder begins to decompose.

If desired,'the friction material may be manufactured so that, in itsfinished state, it contains as binder both a thermosetting resin andnickel sulphide formed from the nickel and the antimony sulphide. Thismaterial can be manufactured by mixing together finely divided nickel, acurable thermosetting resin, and antimony sulphide, compressing themixture, and heating it to a temperature sufiiciently high to cure thethermosetting resin and to cause at least some of the finely dividednickel to combine with at least some of the antimony sulphide to formnickel sulphide.

If extremely high temperatures, for example in the order of 600 C. areused in the curing step of this process, the thermosetting resin isquickly decomposed and carbonised. However, if the reaction is carriedout over a long period at a lower temperature (for example in the orderof 325-400 C.) the thermosetting resin can be cured without totaldecomposition, and at least some of the nickel can be made to combinewith at least some of the antimony sulphide to form a nickel sulphidebinder. During such a slow curing process, the compressed mixture ispreferably held rigidly in a clamped position to avoid distortion of thecompacted mixture. The compacted material, which will generally bemoulded into a desired shape, for example a pad, block or curveddrumbrake lining, can then be incorporated into a power transmission orfriction braking system in a conventional manner and without furthershaping.

If it is desired to manufacture a friction material containing nickel,antimony sulphide and a thermosetting resin with the nickel and antimonysulphide uncombined, the compressed ingredients are usually heated to atemperature of from 120 to 180 C. depending upon the particular resinused. The thermosetting resin may be cured in one stage but ispreferably cured in two stages, first by applying suflicient heat partlyto cure the resin whilst compressing the mixture and subsequentlyheating the mixture after compression in order to complete the curing ofthe resin. Typical heating conditions for the two curing stages are, inthe first stage, 120 to 180 C. for 5 to minutes, and 90 to 300 C. for 2to 24 hours in the second stage. Where the compacted friction materialcontains a thermosetting resin, 2 to 25% by weight of thermosettingresin, 2 to 25 by weight of thermosetting resin will normally be used asa binder with from 3 to 30% by weight of nickel and 2 to by weight ofantimony sulphide. If desired, 5 to 60% by weight of asbestos fibre and/or 5 to 50% by weight of filler may be incorporated.

Our research work has not only shown that nickel and antimony sulphidecan be used in a friction material to supplement the binding action ofnormal thermosetting resin binders but also indicates that nickelsulphide formed from nickel and antimony sulphide can, in combinationwith one or more fillers and/or friction modifiers act as a suitablefriction material by itself. According to this still further aspect ofthe invention, therefore, there is provided a compacted frictionmaterial comprising nickel sulphide formed in situ from finely dividednickel and antimony sulphide, and at least one filler and/ or frictionmodifier. Any of the conventional fillers and friction modifiersmentioned above are suitable for incorporation in this material.Preferably, the friction material further includes an inorganic fibrousreinforcing material such as asbestos.

In order to manufacture the compacted friction material which does notcontain a thermosetting resin binder, finely divided nickel, antimonysulphide and one or more fillers and/or friction modifiers are mixedtogether, the mixture is then compressed and heated to a temperaturesufliciently high to cause the nickel and the antimony sulphide tocombine to form nickel sulphide. At normal pressure, nickel and antimonysulphide react together to form nickel sulphide at temperatures inexcess of 325 C. and, in order to effect speedy reaction of the nickeland antimony sulphide, temperatures in the region of 600 C. willgenerally be required.

The nickel and the antimony sulphide may be heated together in this wayin a wide range of proportions. For example, from 15 to by weight ofnickel may be heated with from 5 to 65% by weight of antimony sulphide.Normally, from 5 to 45% by weight of a filler or friction modifier willbe incorporated in the friction material. 5 to 50% by weight of asbestosfibre may be incorporated as a reinforcing material.

Where a friction modifier is used, the exact amount will depend upon thedesired frictional characteristics of the finished product. For example,from 5 to 25% by weight of barytes may be added to decrease thecoeflicient of friction of the finished material.

The following examples further illustrate the invention:

EXAMPLE 1 Friction material containing nickel sulphide and filler Amixture of 45% by weight of finely divided nickel, 30% by weight ofantimony sulphide, 20% by weight of asbestos fibre and 5% by weight ofbarytes was prepared. The mixture was compressed in a die at a pressureof 15 tons per square inch. The mixture was then removed from the dieand heated in air in a mufiie furnace to a temperature of 600 C. Duringthe heating, the nickel and the antimony sulphide combined together toform nickel sulphide. The resultant material was hard and strong and itsphysical properties were those characteristic of a friction materialsuitable for use in friction braking or power transmission systems.

EXAMPLE 2 Friction material containing nickel, antimony sulphide and athermosetting resin A mixture of the following compounds was prepared:

Ingredient Percent by weight Nickel 20 Antimony sulphide 15 Phenolicresin 15 Asbestos fibre 45 Graphite 5 The material was charged into amould and compressed at a pressure of 1 ton per square inch for 10minutes at C. The material was then removed from the mould, placed in anoven and heated to a temperature of 200 C. for 10 hours. The resultingmaterial contained uncombined nickel and antimony sulphide boundtogether by the phenolic resin and could be used as a friction material.

EXAMPLE 3 Friction material containing nickel sulphide and athermosetting resin A mixture of ingredients as set out in Example 2 wasprepared. The mixture was compressed and heated in a clamped position ata temperature rising from 200 to 400 C. over four hours.

The nickel and antimony sulphide in the original mixture had almostcompletely combined to form nickel sulphide. Some carbonisation of thethermosetting resin had occurred but the bulk of the resin wasundecomposed. The frictional properties of this material werecharacteristic of a material suitable for use in a friction braking orpower transmission system.

We claim:

1. A compacted friction material comprising nickel sulphide formed insitu from 15% to 85% by Weight of finely divided nickel and 5% to 65% byweight of antimony sulphide, and 5% to 45% by weight of at least onematerial selected from the group consisting of fillers and frictionmodifiers.

2.A compacted friction material according to Claim 1 further includingto 50% by weight of a fibrous inorganic reinforcing material such asasbestos.

3. A compacted friction material which comprises a binder having 2% to25% by Weight of a thermosetting resin part and a further part whichconsists of nickel sulphide formed in situ from 3% to 30% by weight offinely divided nickel and 2% to by weight of antimony sulphide.

4. A compacted friction material comprising 3% to 30% by weight offinely divided nickel, 2% to 20% by weight of antimony sulphide and 2%to by weight of a thermosetting resin binder.

5. A compacted friction material according to Claim 3 wherein thethermosetting resin is an organic thermosetting resin.

6. A compacted friction material according to Claim 3 wherein thethermosetting resin comprises an organic thermosetting resin whichcontains inorganic substituent groups.

7. A compacted friction material according to Claim 3 further including5% to 60% by weight of a fibrous inorganic reinforcing material such asasbestos.

8. A compacted friction material according to Claim 3 further including5% to 50% by Weight of at least one material selected from the groupconsisting of fillers and friction modifiers.

9. A method of manufacturing a compacted friction material comprisingthe steps of mixing together 15% to 85% by Weight of finely dividednickel, 5% to 65% by weight of antimony sulphide and 5% to 45% by weightof at least one material selected from the group consisting of fillersand friction modifiers, compressing the mixture, and heating it to atemperature sufliciently high to cause the nickel and the antimonysulphide to combine to form nickel sulphide.

10. A method according to Claim 9 wherein the mixture is heated whilstbeing maintained under pressure in a desired shape.

11. A method of manufacturing a compacted friction material comprisingthe steps of mixing together 3% to by Weight of finely divided nickel,2% to 20% by weight of antimony sulphide and 2% to 25% by weight of acurable thermosetting resin, compressing the mixture and heating it to atemperature sufliciently high to cure the thermosetting resin.

' 12. A method according to Claim 11 which comprises compressing themixture and simultaneously with such compression applying heat partly tocure the thermosetting resin and after its compression further heatingthe mixture completely to cure the resin.

13. A method of manufacturing a compacted friction material comprisingthe steps of mixing together 3% to 30% by Weight of finely dividednickel, 2% to 20% by Weight of antimony sulphide and 2% to 25% by weightof a curable thermosetting resin, compressing the mixture, and heatingit to a temperature sufiiciently high to cure the thermosetting resinand to cause at least some of the finely divided nickel to combine withat least some of the antimony sulphide to form nickel sulphide.

14- A compacted friction material for use in a friction braking or powertransmission system which includes a two part binder system, one partcomprising 2% to 25 by weight of a thermosetting resin and the otherpart comprising a mixture of 2% to 20% by weight of antimony sulphideand 3% to 30% by weight of nickel capable of progressively combiningunder the action of heat developed as a result of the frictionalengagement of the friction material within the braking or transmissionsystem to provide additional binding for the friction material.

15. A compacted friction material according to Claim 14 comprising 5% toby weight of inorganic fibrous material such as asbestos.

References Cited UNITED STATES PATENTS 3,723,382 3/1973 Lumb et al.260DIG. 39 X 3,660,120 5/1972 Clark et al. 106-36 2,252,991 8/1941 Steck10636 3,402,054 9/1968 Wood et al. 106-36 OTHER REFERENCES I. W. Mellor,Comprehensive Treatise on Inorg. and T heor. Chemistry (1922), QD31.m4,vol. 9, p. 525.

MORRIS LIEBMAN, Primary Examiner S. M. PERSON, Assistant Examiner US.Cl. X.R.

106-36; 260DIG. 39

1. A COMPACTED FRICTION MATERIAL COMPRISING NICKEL SULPHIDE FORMED INSITU FROM 15% TO 85% BY WEIGHT OF FINELY DIVIDED NICKEL AND 5% TO 65% BYWEIGHT OF ANTIMONY SULPHIDE, AND 5% TO 45% BY WEIGHT OF AT LEAST ONEMATERIAL SELECTED FROM THE GROUP CONSISTING OF FILLERS AND FRICTIONMODIFIERS.